A prior art method is taught in USSR Inventor's Certificate Specification No. 1260716 for swabbing wells according to which, a heavy swab is run into a well on a hoist cable. Under the influence of its weight the swab goes down in the well and it is sunk below fluid level. The depth of immersion of the swab in the liquid is monitored after which the swab is raised back together with the column of liquid lying above it. This cycle is repeated. After several cycles, when the fluid level in the well ceases to drop, a well production rate is determined. This method can be used during well completion, trial operation or for cleaning out the near-bottom zone of oil and water from the wells.
The shortcomings of the aforementioned patented method consist in its high power consumption, the necessity for using a powerful hoist and a cable of large diameter. These requirements impose physical constraints which limit the utility of this method. It is the weight of the swab and hoist cable that makes up the considerable part of the weight being raised which leads to a reduction in the coefficient of useful utilization of the hoist capacity. In addition to this, the possibility of a gas breakthrough from the formation, when the liquid is being raised, requires the construction of the lowerable assembly to be more complicated, in order to prevent the latter from being jammed and to avert a breakdown of the drive means. It is also dangerous to make use of this method in the wells of gas fields and gas condensate fields.
Another prior art device for raising a liquid from wells, either flooded or gas producing ones, is taught in USSR Inventor's Certificate Specification No. 1161720. The device taught in this patent comprises a hoist, a cable, a lift tubing string, and a plunger which is accommodated inside the string and fastened to the cable. In order to prevent leakages of the liquid, when being raised, this plunger is provided with a sealing and the device includes a special breaking gear in order to prevent it from jamming in case of a gas breakthrough from the formation.
After the raised liquid begins to overflow into the horizontal pipeline located on the surface of the ground, the back pressure on the gas below the device decreases causing the gas to expand. The sealing of the plunger sealing hinders the outflow of gas, and the device gets accelerated to a high speed similarly to a shell accelerating in a gun barrel under the influence of gas pressure when the powder is burning therein. As a result, the flexible pulling member fails, and the device may get jammed in the lift tubing string or destroy the well head equipment by striking it, since the device has a heavy weight. So, operational reliability of the device is accompanied by a substantial complication of its construction.